Thermoelectric power in alloys with phase separation (composites)

Abstract

A thermopower formula is derived for composites: [Formula: see text] (κ(i) and κ are the specific thermal conductivities, S(i) and S are the Seebeck coefficients of the phase i and the composite, respectively, and υ(i) is the volume fraction of the phase i). This formula can be applied for calculating the Seebeck coefficient (thermoelectric power) of amorphous transition-metal-metalloid alloys, for which amorphous phase separation occurs for large ranges of concentration. There are two contributions to S(i), a scattering term and a contribution due to electron transfer between the phases maintaining a common electrochemical potential μ. The theory predicts discontinuities in the concentration dependence of the Seebeck coefficient of metallic composites. It is argued that in amorphous composites these discontinuities occur very precisely at υ(i) = 1/3. This phenomenon can be used to characterize the crystallization kinetics of amorphous alloys. The theory is applied to a- Cr(1-x)Si(x) alloys for calculation of S versus x. Both the calculated S(x) dependence and the discontinuities agree very well with the experimental data, as long as x<0.67; the deviations at x>0.67 are interpreted to be caused by the p-d bonds at the phase boundaries.

Anisotropic layered Bi2Te3-In2Te3 composites: control of interface density for tuning of thermoelectric properties

“…2). Effective medium theory (EMT) and its generalized derivation (GEMT)373839 have been used to predict the thermoelectric properties of composite materials where a randomly distributed secondary phase is embedded in a matrix4041. As to BTIT-7.5 in the present work, strong anisotropy effects in structure and thermoelectric properties were confirmed.…”

“…where f is the volume fraction and k is the total thermal conductivity of the respective constituent phase, A is a constant that depends on the actual percolation threshold (of phase 2 in phase 1) through the equation , t is a constant representing the asymmetry of the microstructure, and the subscripts 1, 2 and e refer to Bi 2 Te 3 , In 2 Te 3 and BTIT, respectively373839.…”

Effective medium theory based modeling of the thermoelectric properties of composites: comparison between predictions and experiments in the glass–crystal composite system Si10As15Te75–Bi0.4Sb1.6Te3

“…17,18 However, having in mind the simple short circuit concept, it seems rather unphysical that electrical conductivity should not play any direct role in the equation of the thermopower for a composite system, especially with a combination of conducting and insulating components. One may argue that the formalism applied to r and l in the GEMT may not be fully valid for l/a.…”

“…16,17 Few years later, replacing the heat flux by the entropy flux, a more general equation was derived, thereby extending the previous model to non-degenerate semiconductors. In 2005 and 2006, Sonntag derived a formula valid for metals or degenerate semiconductors by applying the EMT formalism to the heat flux and chemical potential.…”

Effect of sintering in ball-milled K2Bi8Se13 thermoelectric nano-composites

“…Recently, for composites that consist of different phases, Sonntag [23] proposed the following expression, based on effective medium theory and the Boltzmann transport equation:…”